Measurement of Nucleus Pulposus (NP) Water content by Magnetic Resonance Imaging (MRI):

Introduction: water content of nucleus pulposus (np) is a significant factor in both viscoelastic behavior and age-related degenerative changes. the rate and magnitude of diurnal disc narrowing are caused by loading and its effect on water content. a new and noninvasive method for measuring changes in water content of np in vivo is used to indicate disc compression. methods: mri was conducted on 36 healthy males with no history of back pain. their mean age and sd were 27 and 6.88 respectively (range 20-46). li to si was imaged supine, sitting and standing using an upright 0.6 tesla magnet (fonar melville ny). a set of h2o: d2o calibration phantoms were mounted on the back of subjects. the phantom was made with tl and t2 relaxation time similar to those of tissues in the np. a calibration curve was provided from the h2o: d2o phantoms for each image. this calibration curve was then applied to the absolute proton density image, yielding a pixel-by-pixel map of water %. result: the sitting and standing postures showed highly significant decrease (p< 0.001) in water content of np in all levels compared with supine posture. the np in all level at sitting posture had less water than standing and level of differences were highly significant (p< 0.000). discussion: the results of this study show the variation of np's water content, on mid sagittal mri images, while performing tasks in different postures are in agreement with disc pressure measurements, reported in the literature. in summary, the water content measuring by quantitative mr imaging could become a powerful tool for clinical and ergonomic applications.